You should try to always keep two doors between her and the outside world. Even if that means confining her to a laundry room or bathroom.
I am worried for her kittens as those tomcats could be carrying a disease to pass on to them. I am always worried because of your flea problem. You could still have her spayed right now. If you are unsure about doing that, know that is a commonly done by many people who either find pregnant cats or they have one that slipped out. It is nothing to feel bad about. But it is the responsible thing to do.
If you are having trouble affording flea treatment and saving up money to spay your cat, I am worried that you will be able to make sure the mother gets a highquality kitten food, that she gets tested and her shots if not done already, that you are able to care for her and kittens if she should need an emergency c-section at the ER vet ($$$!) or if she rejects the kittens and they need to be bottle fed every 2 hours and thru the night, then when the kittens are old enough they get their vaccinations and dewormed and all get spayed or neutered before going to new homes which is also a lot of $$$. Spay/neuter can be done at 8 weeks so it is important to have that done before they go to a new home so this problem doesn't continue on. Then you can charge a slightly bigger adoption fee for them to be adopted out.
Please consider spaying the mother now anyways, there is a LOT of time and especially money in raising kittens, especially like I said if you need an ER vet and there is also the risk of her getting pregnant again right after having this litter. I can happen almost immediately. Think about your moving too, that is going to be really stressful on a pregnant or nursing mother. That could be enough to make her reject them right there depending on her motherly abilities.
One last thing, if money is tight for you, we can recommend some low cost clinics for you to get your cats spayed and neutered or a place for you to get the whole future family you may have spayed and neutered for a low cost or sometimes free if you qualify. Just tell us your city and state.